1. Field of the Invention
The present invention relates to a hydroprocessing catalyst, more particularly, to a catalyst suitable for effecting simultaneous hydrodesulphurisation and hydrodemetallisation of sulphur- and metals-containing feedstocks. The invention further relates to a process for the use of this catalyst, and to a process for the preparation thereof.
2. Description of the Related Art
One of the steps in the preparation of ready-for-use products from heavy oil fractions is the complete or partial removal of impurities. Heavy feedstocks, such as feeds based on atmospheric residual oils, vacuum residual oils, tar sand oils, and shale oils generally contain sulphur components and metallic components. These impurities can be removed by contacting the feedstock with a hydroprocessing catalyst at elevated temperature and pressure in the presence of hydrogen. This will cause the sulphur compound to be converted to H.sub.2 S, while the metals precipitate on the catalyst particles.
The catalysts which are to effect this combined hydrodesulphurisation and hydrodemetallisation have to satisfy quite stringent requirements. On the one hand, the hydrodesulphurisation and hydrodemetallisation activity of the catalyst should be high, while on the other, the catalyst should have a long life. It has proven difficult to find a catalyst which satisfies all three demands simultaneously. This is so because these demands are inconsistent among themselves. For example, if one improves the hydrodesulphurisation activity by increasing the metals content of the catalyst, it turns out that this measure is accompanied by a shorter catalyst life.
Alternatively, if one increases the average pore diameter of the catalyst to increase its hydrodemetallisation activity, the resulting lower surface area will lead to decreased hydrodesulphurisation activity.
In the literature, several hydroprocessing catalysts have been proposed to effect simultaneous hydrodesulphurisation and hydrodemetallisation of hydrocarbon feeds, all of which have tried to find the optimum combination of hydrodesulphurisation activity, hydrodemetallisation activity, and catalyst life.
U.S. Pat. No. 4,588,709 has tried to solve this problem by preparing the catalyst by way of a specific double impregnation procedure.
U.S. Pat. No. 3,931,052 describes a catalyst for simultaneous hydrodesulphurisation and hydrodemetallisation with a relatively low surface area, the support of which preferably consists of delta- and/or theta-alumina.
U.S. Pat. No. 5,223,472 describes a catalyst for the simultaneous hydrodesulphurisation and hydrodemetallisation of hydrocarbon feeds, the support of which comprises at least 10 wt. % of delta-alumina and the balance gamma-alumina. However, it appears that none of these catalysts satisfies all the requirements of high hydrodesulphurisation activity, high hydrodemetallisation activity, and a long life. Hence, there is still need for a catalyst composition which combines high hydrodesulphurisation activity with high hydrodemetallisation activity and a long life.